PROJECT SUMMARY The lack of successful regeneration after injury in the mature central nervous system is due to intrinsic and environmental obstacles. Though progress in the field has been made, overcoming these barriers to result in robust functional axon regeneration and recovery is still a significant challenge. We build upon preliminary data and hypothesize that recurrent DREADD-mediated neuronal activation after injury is a means to enhance functional axon regeneration. Additionally, we will test the hypothesis that neuronal activation increases axon regeneration via both mTOR activation and increasing dynamic microtubules. We will these our hypotheses both in vitro using adult dorsal root ganglion neuron cultures and in vivo using dorsal root crush, dorsal columns spinal cord injury (SCI)/peripheral nerve graft (PNG), and incomplete cervical SCI/PNG models. In Aim 1, we will elucidate how repeated, chemogenetic neuronal activation enhances axon regeneration. In Aim 2, we will assess if neuronal activation ? alone or in combination with manipulations that increase dynamic microtubules and mTOR activation ? promotes functional axon regeneration. Collectively, we will: 1) elucidate mechanisms behind how neuronal activation enhances growth, potentially identifying new therapeutic targets; 2) determine the extent to which neuronal activation enhances regeneration in different injury models (dorsal root crush, SCI); 3) determine if neuronal activation has disparate or similar effects in different populations of neurons (DRG vs. CNS); 4) test whether meaningful axonal regeneration is facilitated using a unique, multi-faceted approach that: a) uses chemogenetic neuronal activation ? possibly along with further increasing dynamic microtubules and/or mTOR activation ? to enhance the axonal growth response; b) provides a more growth-permissive environment after an injury (i.e. mitigation of the inhibitory matrix of the glial scar with chondroitinase; transplantation of a PNG into an SCI cavity; chondroitinase digestion of plasticity-limiting perineuronal nets). After the completion of these experiments, we will have identified novel therapeutic avenues to foster functional repair after SCI.